Oxidation process



Oct. 13, 1942- w. o. KENYON EIAL 2,298,387

OXIDATION PROCESS Filed Aug. 25, 1939 REGENERATED TEMPERATURE OXIDES OF NITROGEN\- CONTROL COMPOUND TO BE OXIDIZED REDUCED OXIDES (ALCOHOLAlDEHYDE, KETONE) OX'DES 0F OF NITROGEN mTRoeEq 24 INERT GAS OXIDES or NITROGEN, ggfifi'fi 1 '/UNTREATED MATERIALS, ETc.

OXIDES OF NITROGEN ,coNDENsER PRODUCT Q 17 PRODUCED BY- THE OXlDATION 13 grwe/wto'w Wwmm O.K

Patented Oct. 13, 1942 OXIDATION PROCESS William 0. Kenyon and George Victor Heyl, Roch.

ester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application August 25, 1939, Serial No. 291,910

9 Claims.

This invention relates to oxidation processes for converting various organic compounds to organic acids and more particularly to a continuous process for oxidizing certain oxygen-containing compounds such as alcohols, aldehydes and ketones to acids through selective oxidation by means of oxides of nitrogen as an oxidizing medium.

The organic compounds such as the mono-basic acid butyric acid, or dibasic acid such as, for example, adipic acid and other related compounds, having at least two CH2 groups in the molecule, have various industrial uses. While oxidation processes for the production of these compounds have been suggested, many of these processes are not particularly satisfactory. For example, it has been suggested to employ nitric acid or potassium permanganate as oxidizing mediums. However, the use of such oxidants for the preparation of adipic acid adds to the cost of the acid produced and oxidant is not readily regenerated from the by-products of the reaction. Other of the processes for oxidizing compounds such as butyl alcohol and butyraldehyde to the acid have required rather a substantial number of steps in their operation.

We have found a method for treating oxygencontaining compounds such as alcohols, alde hydes and ketones by a special oxidizing medium which not only is selective in its action, but forms by-products which may readily be regenerated and re-employed.

This invention has for one object to provide an oxidation process particularly adapted to the treatment of oxygen-containing compounds, either aliphatic or aromatic, such as alcohols, aldehydes and ketone. Still another object is to provide a process for converting hydroxy compounds having at least two CH2 groups in the molecule into acids. A still further object is to provide an oxidation process wherein an oxide of nitrogen in effect is a carrier for the oxidation and oxygen or air may be used as the oxidant. A still further; object is to provide a continuous process for the oxidation of organic compounds. Another object is to provide an oxidation process which may be operated over a wide range of temperatures. A still further object is to provide a continuous process in which any of the material which escapes oxidation may readily be separated and returned to the oxidation. A still further object is to provide an oxidation process wherein the products of the reaction may be removed from the zone of reaction so asto decrease the opportunity for undesirable side reaction. A

still further object is to provide an oxidation process wherein the oxidizing medium may readily be regenerated by means of air or oxygen. Still another object is to provide a process particularly adapted to the conversion of compounds such as cyclohexanol and cyclohexanone to adipic acid. A still further object is to provide a process particularly adapted to the conversion of aliphatic alcohols or aldehydes containing 2-24 carbon atoms to the corresponding aliphatic acid. Other objects will appear hereinafter.

We have found that NO: is a particularly excellent oxidizing agent for oxygen-containing compounds. Throughout this application when we employ the term N02 we also intend to embrace other oxides of nitrogen which function in a comparable manner as for example nitrogen tetra-oxide, N204, or various mixtures of nitrogen dioxide and nitrogen tetra-oxide. The NO or N203 formed during the reaction can readily be converted to the N0: by treatment with air, oxygen or other oxidizing medium and immediately be reemployed for further oxidation. Thus, the N02 becomes in efiect, a carrier for the oxidation and oxygen or air is used up as the oxidant. The advantages of being able to easily oxidize oxygen containing compounds such as alcohols, aldehydes and ketones in a controlled manner to obtain certain desired oxidation products as for example organic acids, by our method, wherein the use of expensive oxidants is avoided, will be apparent as the description proceeds.

For a more complete understanding of our invention, as well as for illustrating the preferred manner of operation, reference will be made to the attached drawing forming a part of the present application.

The attached drawing shows a side elevation view somewhat in the nature of a flow sheet, of apparatus arrangement which might be used in carrying out our process.

Referring tothe drawing, 2 represents a container or other receptacle in which is placed the oxygen-containing compound to be treated. Another reservoir or receptacle 3 is provided for the oxidizing medium, mainly the oxides of nitrogen. Suitable temperature controlling means such as jackets 4 and 6 are associated with the containers.

The containers are connected by means of valved conduits l and 8 to the reaction chamber 9.

Reaction chamber 9 is likewise provided with suitable temperature controlling means as for example jacket II. It is to be understood that although jackets have been shown, coils or other devices may be inserted in the column or containers or other means employed for controlling the temperature of the materials'in the different parts of the apparatus. Also, if desired, conduits I and 8 may be caused to terminate in spray mechanisms or other devices for obtaining dispersion or diffusion of the reactants. If the reaction is to be carried out in the vapor phase an open column as indicated is satisfactory. However, if liquid phase conditions are to be employed, or if desired in the vapor phase processes,

- the column 9 may be partially or completely filled with packing material such as pumice, broken glass and the'like, in order to cause the spreading over of a larger surface of the compound to be oxidized. The oxidation column or reaction chamber 9 isconnected by conduit means l2 to the receiver l3.

Valved conduit I4 is provided for draw-off reaction products. Also, associated with the receiver l3 but positioned above the base thereof, is another conduit l6 for drawing off uncondensed materials such as spent oxidizing medium, unconsumed oxides of nitrogen, unreacted organic compounds and oxidation products. This conduit leads to another receiver I! provided with temperature controlling means [8. By means of this construction oxidation product not condensed out in receiver l3 may be removed at H and withdrawn through valved conduit l9.

Another conduit 2| connects receiver I! with the oxidant reservoir 3 and the oxidant regenerator 22. The outlet 23 to the regenerator is connected to a source of oxidizing medium such as air or oxygen (not shown). I

The oxidizing unit 9 may be provided with an auxiliary conduit 24 for the introduction of diluents such as nitrogen, carbon dioxide, steam and the like.

For the purposes of discussing our invention and merely for illustrating one type of oxidation reaction which may be carried out, the following chemical equations are set forth. We appreciate that the processes of oxidation with N: described herein may involve the formation of intermediate nitrogenous derivatives which disappear before the completion of the process. Hence, the equations set forth are only for the purposes of graphically illustrating the starting materials and the product of the reaction.

(The cyclohexanol may be obtained by the catalytic reduction of phenol.)

The schematic equations set forth, as already indicated, are merely for the purposes of illustration. The first step in our oxidation process may be the formation of an aldehyde or ketone. For example, when treating cyclohexanol it may be that cyclohexanone forms because, as seen from the equations, both of these compounds yield adipic acid by oxidation with N02.

- the oxide of nitrogen employed, we embrace the Although 7 we have indicated the use of N02 to describe mixture of nitrogen dioxide and nitrogen tetraoxlde which may exist at the particular temperature of the reaction, as shown by the following equation ZNOzfiNaOc.

Likewise, in the equations we have indicated that nitric oxide (NO) is the by-product of this reaction. It is possible, however, that with an excess of NO: the by-products may be N203 (NO+NO2) but since both of these constituents can be reoxidized by air or oxygen to NO: it is believed sufficient merely to indicate that nitric oxide is the by-product.

It is not necessary to use pure NO: as the oxidant since the other constituents such as NO, N203 and the like apparently do not. interfere with the process. The oxides of nitrogen may be obtained commercially, for example, by the nitrogen fixation process or by the oxidation of ammonia.-

Referring to our apparatus, the operation thereof will be generically described in order to avoid unnecessary repetition in the description of the numerous specific examples set forth hereinafter. The organic compound to be oxidized is placed in tank 2 and brought to the desired temperature by circulation of either a cooling or heating medium through jacket 4. The compound is introduced at the desired rate into the oxidation chamber 9 by suitable control of the valve in conduit 1.

The oxidizing medium (liquid N02) is placed in the reservoir 3 and maintained in the liquid state by circulation of cooling medium through the jacket 6. Its rate of flow into the reaction chamber 9 may be governed by the valve in conduit 8.

The compound to be oxidized and the N02 (which, as indicated above may contain other constituents) are introduced concurrently into the reaction chamber 9 at the desired ratio of the two components. We have found that these ratios may be readily changed over wide limits.

The reaction chamber 9 is maintained at the desired temperature by passage of steam or other medium through the jacket ll. Likewise, we have found that the temperature of the reaction may be varied over wide limits. Those compounds which tend to resist oxidation may be heated to a higher temperature than those compounds which oxidize more readily. The various temperatures to employ will be apparent from the several detailed examples set forth hereinafter.

. If desired, the oxidation chamber may be maintained at such a temperature that all of the constituents therein arein the vapor phase and in thismanner cause the reaction to take place in the vapor phase.

We have found it is possible to run the reaction at a temperature somewhat below the boiling point of the compound to be oxidized. Under such conditions the liquid material to be oxidized is introduced into the reaction tube where it comes in contact with the gaseous N02 and is thus oxidized. Under such conditions it may be desirable to place inert solids such as pumice or broken glass into chamber 9 in order to spread the components over a larger surface and facilitate the contact with the N02.

The oxidation product as well as any unchanged compound, N02 and spent oxidizing medium pass into the receiver l3 where the oxidation product is collected. The gaseous products, chiefly oxides of nitrogen, pass through the conduit I6 into contact with condenser l8 where residual amounts of oxidation product may be condensed out.

The oxides of nitrogen, unreacted compound, etc., may be conducted through conduit 2| into the regenerator 22, where any N02 is condensed out and passes into receptacle 3. Air, oxygen or other oxidizing medium is introduced into the regenerator at point 23 where it re-oxidizes the lower oxides of nitrogen to N02 which is condensed and returned to receptacle 3 for use in further oxidation. If desired, an inert gas such as nitrogen or carbon dioxide may be introduced into the reaction through conduit 24.

The products of the reaction collected in receivers I3 and I! may be withdrawn therefrom through conduits l4 and It! to distillation or other treatment. changed starting material may be separated and returned to the container 2 for feeding to the process. Such return may be in a continuous manner.

In connection with the aforementioned equations, the following observations have been made. Dry liquid N02 was added dropwise to about a gram of cyclohexanone in a test tube. ture became green and spontaneously became warm. The mixture was cooled and a few more drops of the N02 added. Again this was allowed to stand until the reaction was completed. Similar procedure was repeated until the addition of the N02 had little or no effect on the mixture. The reaction mixture was then warmed to cause the removal of any oxides of nitrogen leaving a viscous yellow syrup as a residue. This residue was crystallized and tested giving a melting point of 150151 0., thereby indicating the formation of adipic acid.

In another instance dry liquid N02 was added dropwise to about a gram of cyclohexanol in a test tube. As in previous instances, the product became green and spontaneously became hot, evolving oxides of nitrogen and discharging the green color. The addition of N02 followed by cooling, etc., as described, was repeated until the further addition of N02 had little effect. The resultant product was subjected to distillation for removing excess cyclohexanol. A colorless crystalline product was precipitated from the reaction mixture and recrystallized from hot water. The melting point of this product was 150-151 C., indicating the formation of adipic acid.

In this instance about 5 grams of cyclopentanone were dissolved in 30 cc. of carbon tetrachloride. This solution was kept well stirred and a solution of 9 g. of dry liquid N02 and 30 cc. of carbon tetrachloride was added slowly. The resultant solution was allowed to stand for a few hours, the temperature rising to about 40 C. and a slow evolution of gas bubbles took place. A light yellow crystalline material was present in the reaction. This crystalline material was extracted with a hot benzene solution and filtered. The filtrate on cooling precipitated colorless crystals of glutaric acid which were filtered ofi, washed and dried, and recrystallized. This glutaric acid product was tested and appeared to be about 98.8% pure. Similar observations were noted for substituted cyclohexanols, substituted cyclohexanones, decahydro-aand p-naphthols and analogous compounds. The use of carbon tetrachloride as described may be modified by comparable or supplemental use of carbon tetrabromide, tetrachloroethane, aliphatic acids, etc. From the foregoing it was observed that oxides In such treatment any un'' The mixof nitrogen may be caused to selectively oxidize and not nitrate, various organic compounds.

We have found that particularly satisfactory results may be obtained by carrying out the oxidation processes with oxides of nitrogen in a special continuous manner, as for example in the apparatus for continuous operation shown in the attached drawing. It is understood that while we prefer to employ the special arrangement shown in the drawing for carrying out our continuous process, our invention is not to be restricted exactly thereto. The operation of our preferred process will be apparent from the following examples which are set forth for the purposes of illustrating various compounds which may be continuously treated and other features of our process and are not to be considered a limitation thereof.

Example I.-Approximately gm. (1 mol) of cyclohexanol were placed in tank 2 of an apparatus similar to that described in the drawing. Approximately 230 gm. (5 mol) of liquid N02 were placed in tank 3. The reactants were introduced into the reaction chamber 9 which was heated to about C. The rates of addition were adjusted so that the entire amount of each component was introduced during a reaction period of 2 hours. A stream of dry nitrogen introduced through conduit 24 was also passed through the apparatus during oxidation. The oxidation product, namely, adipic acid, which collected in the receiver l3, was withdrawn through conduit l4 and dissolved in hot water, thereby permitting its separation in a crystalline condition by cooling of the aqueous solution. In this way three fractions totalling about 90 grams or 61.6% of theory, based on the amount of cyclohexanol were obtained. The melting point of the adipic acid was 151.5 and a mixed melting point with high-grade adipic acid produced no depression. Therefore, adipic acid of particularly good quality was obtained.

In this example and subsequent examples the yields shown represent the conversion obtained on one pass through the apparatus and no correction was made for the compound which is unchanged and can be recirculated in a second cycle, thereby improving the yields.

Example II.-About 100 grams of cyclohexanol (1 mol) and 184 grams (4 mols) of nitrogen dioxide were reacted during the course of two hours at an average reaction temperature of C. 82.8 grams of adipic acid were obtained after recrystallization in water, which represents a 56% yield, based on the cyclohexanol used. The recrystallized adipic acid melted at 152 0.

Example III.-The amounts of reactants employed were the same as those of Example I. The reaction time was three hours and the average reaction temperature was 108 C. 88.5 gm. of adipic acid were obtained which represents 60% of the theoretical. The recrystallized adipic acid possessed a melting point of 150 C.

Example IV.-Ninety-eight gm. of cyclohexanone (1 mol) were oxidized during a two-hour reaction period with 230 gm. (5 mols) of N02 at an average reaction temperature of 118 C. Fifty gm. of recrystallized adipic acid were obtained, representing 34% of the theoretical. The adipic acid, after recrystallization, melted at 151 to 152 C.

Example V.-Ninety-eight gm. (1 mol) of cyclohexanone were oxidized with 368 gm. (8 mols) of N02 at an average reaction temperature of 92 C. The time required for the addition of the reactants was 3 /2 hours. Seventy-six gm. of recrystallized adipic acid were obtained which represents 52% of the theory. The adipic acid thus obtained melted at 150 C. 7

Example VI.One hundred gm. of cyclohexanol (1 mol) were treated with 359 gm. (7.8 mols) of NO: at an average reaction temperature of about 90 C. The time required for the passage of the reactants through the reaction chamber was 3 hours. 128 gm. of recrystallized adipic acid were obtained, representing 87.6% of the theoretical. The adipic acid melted at 151 C.

The reaction temperatures given in this example represent the temperatures which prevailed during the major portion of the operation. Certain variations of temperature occurred during the reaction, as at the initiation due to variations in the rate of introduction of the reactants and other factors which has not reached equilibrium at the start of the process.

It is apparent from the preceding examples that excellent yields of adipic acid may be obtained from either cyclohexanol or cyclohexanone during one passage through our apparatus. As indicated, these yields may be further increased by recycling the unused reactants. In the operation of our process in certain instances it maybe desirable to limit one or the other of the reactants in order that the reactant present in the smaller amount may be entirely consumed and excessof thev reactants may be recirculated with new feed. In the examples described, nitrogen was passed through the oxidation apparatus but if desired, oxygen or oxygenated dry air may be passed through in order to reoxidize the nitric oxide as rapidly as it is produced.

There are various other compounds which may be treated by our process for the production of substantial yields of oxidation product. For ex ample, aromatic compounds such as benzyl alcohol or benzaldehyde may be readily oxidized to benzoic acid as shown in the following examples.

Example VII.Approximately 108 gm. (1 mol) of benzyl alcohol was placed in tank 2 of an apparatus similar to that shown in the attached drawing. Steam was passed into the temperature controlled jacket around the tank in order to preheat the benzyl alcohol. Approximately 276 gm.

of liquid NO: (6 mols) were placed in tank 3.

The reactants were introducedjnto the reaction chamber 9 simultaneously in the approximate flow ratio of 1:3. The reaction chamber was heated to approximately 100 C. At the end of three hours during which time a very slow current of carbon dioxide had been passed through the reaction chamber, the reactants had been passed through the apparatus. The reaction product was shaken with 400 cc. of carbon tetrachloride. The benzoic acid, traces of unattacked benzyl alcohol and benzaldehyde dissolved in the solvent from which the benzoic acid was removed by shaking with a sodium hydroxide solution. The alkaline solution resulting was heated to boiling, acidified and cooled, whereupon the benzoic acid crystallized out. A yield of approximately 37 grams (or approximately 30%) ofbenzoic acid having a melting point of about 123 C. was thus obtained. From the carbon tetrachloride solution was recovered 59 gm. (55.6%) of benzaldehyde.

Upon returning this recovered benzaldehyde through the apparatus for reoxidation, a con-.

siderably larger yield based on the benzyl alcohol was obtained.

Example vIlL- -commercial vanadium pentoxide was fused for 1 hour at 800 C. and broken up into pieces about the sizev of a pea. The oxidation chamber was packed with successive layers of glass beads,'glass wool, and the granulated vanadium pentoxide.

108 gm. of benzyl alcohol were placed in tank 2 and preheated as in Example VII. 99 cc. (128 gm. or 2.8 mols) of liquid N02 were placed in reservoir 3. The rate of flow of the two reactants was regulated so as to terminate the oxidation in three hours, maintaining an average reaction temperature of 98 C.

By separation of the products as described in Example VII 44' gm. (36% of theoretical) of benzoic acid of M. P. 123, and 40 gm. (37.8%) of benzaldehyde were obtained.

Ezrample IX.The reaction chamber was charged with layers of glass beads, glass wool and vanadium pentoxide as described above. 106 gm. (1 mol) of benzaldehyde were'oxidized with 119.6 gm. (2.6 mols) of N02 at an average temperature of 96 C. over a period of 3 hours in the presence of vanadium pentoxide as described in Example VIII.

The reaction product was well shaken with two 250 cc. portions of carbon tetrachloride. The solvent, now containing the benzoic acid, the aldehyde and possibly other products of minor importance, was heated for a short time with 25% HCl to decompose any nitrites, the acid removed and the carbon tetrachloride solution shaken well with 350 cc. of 5% sodium hydroxide solution andthe benzoic acid recovered from the alkaline solution as in Example VII. The yield of benzoic acid, melting at 123.5 was 50 gm. or 41% of the theoretical. 'From the carbon tetrachloride solution was obtained, by fractional dis tillation, a 36% return of benzaldehyde having a two degree boiling range.

In Examples VII, VIII and IX, a weak current of carbon dioxide was passed through the reaction chamber. However, if desired, oxygen oran oxygenated dry air may be passed through, in order to continuously reoxidize the nitric oxide to dioxide as rapidly as produced. Also, in the examples described, the compound to be oxidized was introduced into the reaction chamber in a preheated but liquid condition and the oxidant in the gaseous state. However, if desired, the compound to be oxidized may be conveniently heated sufficient to cause its vaporization at atomization in which case the alcohol or aldehyde will react more quickly with the nitrogen peroxide. If desired, the nitrogen peroxide too may be atomized.

While the aforementioned examples are illustrations of our preferred embodiment, our process may be applied to the oxidation of a number of other compounds comprising alcohols, aldehydes and ketones. Some of these additional compounds which may be mentioned are decahydronaphthols, cyclohexanols, methyl cyclohexanols, and other substituted or derivative oxygen-containing compounds.

Not only may aromatic oxygen-containing compounds such as aromatic alcohols, aldehydes and ketones be selectively oxidized with nitrogen peroxides, but we have found that there are a number of aliphatic oxygen-containing compounds which may be selectively oxidized into valuable oxidation products. Examples of our process applied to some ofthese aliphatic compounds are as follows:

Erwmple X -74 gm. (1 mol) of n-butyl alcohol were placed in tank 2 of an apparatus similar to .discharged into 250 cc. of cold water.

that described herein. 276 gm. or 192 cc. of liquid N: were placed in reservoir 3. Steam was introduced into chamber ll surrounding the reaction tube 9 and the' reactants were introduced simultaneously in approximate flow ratio of 1:4 which caused the temperature inside the reaction chamber to fluctuate between 104 and 108 C. At the end of five hours, the oxidation was complete and the accumulated reaction product was While stirring, the reaction mixture was treated with caustic soda until a pH of 4 was measured. The reaction mixture was then neutralized with sodium bicarbonate. 1500 cc. of ethylene chloride were then added and the whole was distilled until the distillate was free ,from water. The residue, now a crystalline mass, was shaken out with hot ethylene chloride. The liquid was filtered. and the butyric acid was obtained from it by distillation, using a high column. A yield of 28 gm. (31.8% of theory) of n-butyric acid was obtained, which boiled at 159 to 165 C. This method of isolating the butyric acid could be replaced by other methods, on a commercial scale, and we believe that higher yields of butyric acid would be obtained.

Example XI.72 gm. (1 mol.) of n-butyraldehyde were placed in tank 2 of the apparatus referred to in Example X. 138 gm. of liquid nitrogen peroxide (96 cc. or 3 mols. of N02) were placed in reservoir 3. The reactants were united under the same conditions as described in Example X herein, except that the flow was slightly faster so that the oxidation could be terminated at the expiration of four hours. The reaction temperatur prevailing during the oxidation was between 100 and 108 C. At the end of four hours the reaction mixture was rendered alkaline (pH 10 to pH 9) with caustic soda and steam distilled to remove the unconverted aldehyde. The residue was then treated as described in Example X. A yield of 34 gm. (38.6% of theoretical) of butyric acid of boiling point 162-165 C. was obtained. The identity of the oxidation products of Examples X and X! as butyric acid was established as follows:

1. By observation of the boiling point, as reported above. The literature gives 163.5" C. as the boiling point of n-butyric acid.

2. By titration with alkali, the products isolated from Examples X and XI were found to be 95.2% and 94.4% butyric acid, respectively.

3. By condensation with aniline to form butyranilide, melting at 94 C. and 96.5 C. respectively. The melting point is reported in the literature as 96.

Example XII.94 gm. of n-dodecyl (0.5 mol.) were placed in reservoir 2 of an apparatus similar to that described herein. 276 gm. (199 cc. or 6 mols.) of liquid nitrogen peroxide (N204) were then placed in tank 3. Steam was passed through jacket 4 for several minutes; then the dodecyl alcohol and the nitrogen peroxid were gradually introduced to react in chamber 9. The inside temperatures quickly rose to 110 C. around which point it remained for the duration or the oxidation, which was about 6 hours. vThe reaction product in chamber l3 was then diluted with 300 cc. of hot water and the mass discharged into a large vessel and slowly neutralized while heating to 95 C. About 30 gm. of sodium hydroxide were used for this neutralization. 36 gm. of calcium chloride, dissolved in 150 cc. of water were then added and the reaction product cooled to about C. The separated calcium salt or the acid formed by our oxidation was filtered at the pump, washed with hot water, then with cold water. and finally with acetone. The wet calcium salt was then stirred into a slurry with 500 cc. of hot water and th free acid was liberated by the addition of 200 gm. of concentrated hydrochloric acid. The free lauric acid, an oil while hot, was separate from the calcium chloride solution, dried over anhydrous sodium sulphate at 60 C., and distilled in vacuo. We distilled our oxidation product at a pressure of 0.154 mm. of mercury at which we had calculated, from the boiling points recorded in the literature at other pressures, that lauric acid should distill at a temperature of 115 C., which it did. We obtained a yield of 69% of crude lauric acid. After vacuum distillation, the yield of material melting at 43 C. was 50% of theory. The purity of this product was indicated by titration with alkali to be 92%. and after recrystallization from 75% alcohol, 97.2%.

Example XML-186 gm. of n-dodecyl alcohol (1 mol.) were placed in reservoir 2 of an apparatus similar to that described herein. 460 gm. or 320 cc. of liquid NO: were then placed in tank 3 and the two components allowed to react in chamber 9 which, as described above, had previously been heated by steam. The oxidation was complete in six hours, when the reaction product was discharged into 300 cc. of hot water' made alkaline by the addition or 33 gm. of sodium hydroxide and steam distilled. The unchanged n-dodecyl alcohol was recovered from the distillate by extraction with ethylene chloride and was found to represent 35% of the original amount used, showing that 121 gm. had been oxidized. The residue from the steam distillation was acidified while still hot, the free lauric acid separated from the salt water, dried over anhydrous sodium sulphate at 60 C., and vacuum distilled at a pressure of 0.154 mm. of mercury, yielding 127.5 gm. of lauric acid which, on recrystallization from dilute alcohol, had a melting point of 433 C. and a titration value of 96%. 127.5 gm. of lauric acid represents a yield of 63.8% of the theory.

In Example -XII of this application, we described the oxidation of lauryl alcohol with special reference to the isolation or the lauric acid formed. In this example we again described the oxidation of the alcohol but emphasized the recovery of unattacked dodecyl alcohol by steam distillation of the alkalinized reaction product and subsequent extraction of the distillate with ethylene chloride. In this manner, we recovered 35% of the alcohol originally used. In Example XIV we shall describe a simplified method of recovering the dodecyl alcohol which escaped our oxidation.

Example XIV.The reaction product of an oxidation such as was described in Example XII was diluted with 500 cc. of cold water per 0.5 mol of alcohol used. 35 gm. of caustic soda dissolved in cc. of water were then added while vigorously agitating the solution. This gave a pH of 12. The solution was then chilled to 10 C. and an aqueous calcium chloride solution containing 50 gm. of calcium chloride was added with rapid stirring. A soft material separated. The salt water was decanted and the mixture of calcium laurate and dodecyl alcohol was extracted with 1000 cc. of acetone by refluxing with mechanical agitation for 12 hours. The material was then filtered while hot, washed with boiling acetone, and most of the acetone was distilled oil, leaving 300 cc. of the acetone ex- (a) Dodecyl alcohol used 93 gm.=0.5 mol.

(1)) Dodecyl alcohol recovered (c) Dodecyl alcohol reacted- 19.7 gm.=0.106 mol 73.3 gm.=0.394 mol (d) Laurie acid obtained,

crude 69.0 gm.=0.345 mol (e) Lauric acid, vacuum distilled 63.0 gm.=0.3l mol The yield of purified lauric acid, based on the dodecyl alcohol not recovered, was 80% of the theoretical.

Example XV.--l21 gm. of cetyl alcohol (0.5 mol) were placed in tank 2 of the apparatus as described, and preheated by passing steam through jacket 4. 115 gm. of liquid N02 contained in reservoir 3 were slowly dropped into the preheated (by steam) chamber 9, while the cetyl alcohol was dropped at even a slower rate into the chamber. While the reaction of the two components was carried on at a slow but steady rate of speed, the reaction temperature rose from 100 C. to 110 C., then fluctuated between 105 C. and 110 C. until both components were used up. The receiver was not cooled. The reaction product was diluted, neutralized, and

while heated nearly to boiling was acidified with acetone. By distilling off the acetone, 28 gm. of

cetyl alcohol were recovered. No palmitic aldehyde was found.

The palmitic acid was liberated from its caleium salt as previously described, and thepalmitic acid was dried and distilled in vacuo. The yield of crude acid was 78%, and the yield of vacuum distilled palmitic acid was 72.6% of theoretical. The melting point of the distilled acid was 62-64 C. The literature reports 63-64 C.

From these and the previously described examples, it is apparent that nitrogen peroxides are general oxidants for compounds having an alcoholic hydroxyl group, it having been shown that cyclohexanol may be oxidized to adipic acid and benzyl alcohol to benzoic acid. It has also been shown that cyclohexanone and benzaldehyde respectively may also be oxidized in a similar manner to the same acids. Not only has it been shown that aromatic and cyclic compounds may be oxidized, but it has also been shown that normal alcohols and aldehydes may be easily oxidized by our method to their corresponding acids. Our invention also embraces the oxidation of secondary aliphatic alcohols such as methyl, n-hexyl carbinol and the corresponding methyl n-hexyl ketone. It also includes the oxidation of branched chain aliphatic primary alcohols such as 2-methyl pentanol-l and 2-ethyl hexanol or the, corresponding aldehydes 2-methyl pentanal-l and 2-ethyl hexanal. Halogen substituted alcohols such as p-chloro ethyl alcohol may also be oxidized by this process. The examples which are submitted hereinafter illustrate the oxidation of a secondary alcohol derived from a normal hydrocarbon and also the oxidation of the corresponding ketone. Data on the oxidation of a branched chain primary alcohol and the corresponding aldehyde are also included. The apparatus and general method are as have been described in the preceding examples.

Example XV.0.77 mole of methyl n-hexyl carbinol (100 grams) were reacted with 5 moles of N02 at a temperature of 190 to 200 C. The compounds were fed into the apparatus during a period of 5 hours. The alcohol used has a boiling point of 179 and, at the reaction temperatures employed, the reaction should occur in the vapor phase. From the reaction product, n-heptylic acid was isolated. The yield of acid in the crude state was 70% of the theoretical, calculated on the basis of the amount 01 alcohol which was run through the cycle. Alter purification of the crude acid by distillation, 'a yield of 67.2% was obtained. For purposes of identification, a portion of the product was converted into the amide which melted at 93 to 94 C. The literature records the melting point of n-heptylamide as 93 to 95 C.

In addition to the heptylic acid formed, we recovered an amount of unchanged methyl n-hexyl carbinol which corresponds to 19% of that used in the example. 021 the basis of the amount of carbinol actually entering into the oxidation, the yield of purified acid is 83%.

Example XVI.--0ne mole of methyl n-hexyl ketone (128 grams) was passed through the reaction apparatus during a. period of 5% hours concurrently with 6 mols of N02. The reaction temperature was 190 to 200 C. and, since the ketone boiled at 172 C., the reaction components were in the vapor phase. Seventy-three grams of crude heptylic acid were isolated from the reaction products and from this, 68 grams of nheptylic acid, purified by distillation, were obtained. This represents a yield of purified acid of 52.3% based on the input of theketone. 26% of the ketone passed through the apparatus was recovered as unreacted material. This means that 94.7 grams of ketone were actually used and, on this basis, the 68 grams of pure heptylic acid obtained represent a yield of 70.7% of the theoretical. A portion of the purified heptylic acid was converted into the amide which melted at 93 to 94 C. The literature gives 93 to 95 C. as

the melting point of n-heptylamide.

Example XVII;-0.5 mol of 2-ethyl n-hexanol (65 grams) was passed through the reaction apparatus during a'4-hour pediod with 3 mols of N02. The reaction temperature was C. which is below the boiling point of the 2-ethyl n-hexanol. From the reaction product, a crude 2-ethyl n-caproic acid was obtained which was purified by distillation, giving 30.5 grams of purified product which represents a yield of 42.3% of theory based on the input of the alcohol. A portion of the purified acid was converted into the amide which possessed a melting point of 102 to 103 C. A mixed melting point of this amide with an authentic sample of the amide prepared from known 2-ethyl n-caproic acid was 102.5 to 103 C.

Seventeen grams of unreacted alcohol were recovered from the reaction mixture. This indicates that 48 grams of the alcohol were oxidized. On this basis, the yield of purified 2- ethyl n-caproic acid was 57.2%.

Example XVIII.--0.5 mol of 2-ethyl n-hexaldehyde (64 grams) was run through the reaction a yield of purified material of 58.3%. of the distilled acid was converted to the amide chamber at a temperature of 100 C. during the course of four hours with'the concurrent addition of 3 mols'of N02. From the reaction product there were obtained 56 grams of 'crude 2- ethyl n-caproic acid which yielded 42 grams of purified acid after distillation. This represents A portion which melted at 102.5 to 103 C. A mixed melting point of this amide with an authentic sample of the amide of 2-ethyl n-caproic acid was 102.5 to 103 C.

From the reaction mixture there were isolated 19.2 grams of unchanged 2-ethy1 n-hexaldehyde. Subtracting this from the 64 grams which were run through the cycle, 44.8 grams of the aldehyde were actually converted and, on this basis, the yield of acid is 83.3%. It is therefore apparent that our process may be applied to a wide variety of oxygen-containing compounds.

In some examples, we have introduced the compound to be oxidized into the reaction zone in the liquid state. However, we may introduce the compound by spraying, thus producing a fine mist which will more readily react with the N02. If desired, theNOz may also be introduced as a mist by spraying.

As already indicated, when we employ the term this oxide of nitrogen, as well as other oxides of nitrogen. In the aforementioned examples we have described the introduction of air an oxidizing medium because this is an economical methd of regenerating the nitrogen peroxides, and we have found that moist air is particularly efficacious for this purpose. However, oxygen, ozone or various other sources of oxygen may be employed for regenerating the nitrogen peroxides. It will also be observed that our process may be operated with or without the various solid oxidation catalyst material, as for example, oxides of vanadium. Other refractory metal salts from the sixth, seventh and eighth groups of the periodic system may be employed in place of the vanadium catalyst.

Our process possesses a number of advantages. For example, not only may various organic compounds be oxidized, but the desired oxidation products'may be obtained in substantial yields. The process may be operated continuously and the oxidant (N02) may readily be recovered and economically re-oxidized and re-used. Furthermore, in our novel process excess oxidant as well as spent oxidant do not present problems of separation but may readily be removed from the oxidation products for regeneration and reuse in the process. Likewise, unconsumed organic compounds may be readily recovered and re-utilized in our process.

It is apparent from the foregoing that our invention is susceptible of some modification. Hence, we do not wish to be restricted excepting insofar as may be necessitated by the prior art and the spirit of the appended claims.

What we claim and desire to be secured by Letters Patent of the United States is:

1. A continuous process for the production of acids by the treatment of oxidizable oxygen-containin compounds from the group consisting of alcohols, aldehydes, and ketones, which comprises continuously feeding said oxygen-containing compound into a reaction zone, continuously feeding into the reaction zone an oxidant comprising substantially all N 02 free of water, maintween 35 C.-275 C. for causing the oxidation of at least a part of the compound by means of the N02, withdrawing a part of the reaction product, separating oxides of nitrogen therefrom, returning separated oxides of nitrogen to a re-oxidation process for the regeneration of N02, by oxygenated dry air and employing a part of this regenerated N02 for the aforementioned continuous feed.

2. A process for the production of acids by the oxidation of straight chain oxidizable oxygencontaining compounds from the group consisting of alcohols, aldehydes, and ketones, which comprises subjecting said compound to reaction with an oxidant consisting of N02 at a temperature between 30-300 C. wherein at least a part of the compound is oxidized to a corresponding acid, and separating at least a part of the oxidation product containing the acid.

3. The oxidation process for the production of acids which comprises treating oxidizable compound; from the group-consisting of alcohols, aldehydcs and ketones with an oxidant comprising substantially all dry N02, separating at least a part of the unconsumed and spent oxidant from the acid oxidation products produced, treating the oxidation product with water and alkali, cooling the resultant aqueous solution, adding a hygroscopic salt to the solution whereby the salt of the acid is precipitated, separating the aqueous salt water and extracting the residue with a solvent for the salt of the organic acid remaining, and recovering at least a part of the organic acid contained in said salt.

4. A process for the production of acids by the treatment of oxidizable compounds from the group consisting of alcohols, aldehydes, and ketones, which comprises continuously supplying said compound to a reaction zone into the presence of an oxidant substantially all N02 free of water also continuously supplied thereto, maintaining the reaction zone at a temperature between 30 C.-275 C., to cause an oxidation reaction to take place wherein at least a part of the compound is converted to organic acid, withdrawing reaction materials and separating at least a part of the oxidation product containing organic acid.

5. The oxidation process for the production of acids which comprises continuously feeding at least one oxidizable compound from the group 1 consisting of alcohols, aldehydes, and ketones,

taining the reaction zone at a temperature becontinuously into a reaction chamber and continuously feeding an oxidant essentially comprised of N02 free of water into the chamber and into intimate contact with the compound, maintaining the reaction chamber temperatures between about 50 C.-325 C. to cause oxidation reaction to take place, wherein part of the compound is converted to organic acid, withdrawing the reaction mixture containing organic acid and separating unconsumed and reduced oxidants therefrom, withdrawing and separating at least a part of the organic acid from the oxidation product, passing the separated oxidant and spent oxidant to a regeneration treatment with air for reconverting the reduced oxidant to active oxidant, returning the active oxidant to the process and during at least a part of the process introducing an inert gas into the reaction.

6. The process for the production ofacids which comprises continuously introducing an oxidizable alcohol into a reaction chamber, continuou'sly introducing an oxidant comprised substantially all of N02 free of water into the chemher and into intimate contact with the alcohol, maintaining the reaction chamber at a temperature above 90 C; but below 400 0., whereby at least a part of the alcohol is converted to acid, withdrawing at least a part of the reaction mixture containing acid and separating the acid therefrom.

7. The oxidation processfor the production of acids which comprises oxidizing an oxidizable compound from the group consisting of alcohols, aldehydes, and ketones with an oxidant comprising substantially all NO: free of water, separating at least a part of the unconsumed and spent oxidant from the acid oxidation products produced, treating the oxidation product with water and alkali, cooling the resultant aqueous solution, adding to the solution a salt of a metal which forms a substantially insoluble salt of the organic acid produced, whereby certain materials containing unused organic starting material and the salt of 'the organic acid are precipitated, separating the aqueous salt water and extracting the residue with a solvent for the unused organic starting material, and recovering at least a part of the organic material from the extract and at least a part of the organic acid contained in said salt.

8. The process for the production of acids which comprises continuously introducing an oxidizable ketone into a reaction chamber, continuously introducing an oxidant of oxides of nitrogen substantially all N02 free of water, into the chamber and into intimate contact with the keton, maintaining the reaction chamber at a temperature above C. but below 400 C. whereby at least a part of the ketone is oxidized, withdrawing at least a part of the reaction mixture containing oxidation product and separating the oxidation product therefrom.

9. The process for the production of acids which comprises continuously introducing an ox idizable aldehyde into a reaction chamber, continuously introducing an oxidant of oxides of nitrogen substantially all N02 free of water, into the chamber and into intimate contact with the aldehyde, maintaining the reaction chamber at a temperature above 90 C. but below 400 C. whereby at least a part of the aldehyde is oxidized, withdrawing at least a part of the reaction mixture containing oxidation product and separating the oxidation product therefrom.

WILLIAM O. KENYON. GEORGE VICTOR HEYL. 

